Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $53.74   12.473%   $60.443   $60.44   $60.45   $60.40  
  Purchase #2 $171.46   11.136%   $190.5538   $190.55   $190.55   $190.60  
  Purchase #3 $139.71   6.832%   $149.255   $149.26   $149.25   $149.30  
  Purchase #4 $111.76   3.418%   $115.58   $115.58   $115.60   $115.60  
  Purchase #5 $208.28   8.102%   $225.1548   $225.15   $225.15   $225.20  
  Purchase #6 $161.49   11.793%   $180.5345   $180.53   $180.55   $180.50  
  Purchase #7 $135.42   7.351%   $145.3747   $145.37   $145.35   $145.40  
  7 purchase totals = $981.86       $1,066.8958   $1,066.88   $1,066.90   $1,067.00